1. Field of the Invention
The present invention is directed to a method of and apparatus for forming a coating having at least one fade zone on a surface of an article and, more particularly, to a method of and apparatus for pyrolytically depositing one or more metal oxide coatings having at least one fade zone on a portion of a moving float ribbon of glass. The present invention is also directed to articles having a coating formed over a surface of the article, which coating includes at least one fade zone, particularly articles made from the above-described coated float glass ribbon.
2. Description of the Prior Art
As used herein, the term xe2x80x9cfade zonexe2x80x9d refers to an area or zone of a coated article, e.g. a coated substrate, having a first limit spaced apart from a second limit, in which a coating present over the substrate within the zone gradually decreases in thickness, intensity and/or density from a first thickness, intensity and/or density at the first limit to a second lesser thickness, intensity and/or density at the second limit. The term also refers to an area or zone in which a coating present over the substrate gradually decreases in thickness, intensity and/or density from a first thickness, intensity and/or density at a first limit to an absence of coating over the substrate at a second limit. Such coatings may also be referred to as xe2x80x9cgradedxe2x80x9d or xe2x80x9cgradientxe2x80x9d coatings.
It is known to form a coating having a fade zone over a substrate. For example, U.S. Pat. No. 3,004,875 to Lytle discloses applying a band of metal salt composition at an oblique angle toward an edge portion of a substrate to be coated, using a shield to limit the area of application of the coating composition. The resulting band is of gradually increasing intensity from its boundary portion adjacent to the edge of the shield because of eddies that evolve beneath the shield near the edge of the shield during the coating operation.
Also, for example, U.S. Pat. No. 2,676,114 to Barkley discloses various methods of producing graded coatings by vacuum deposition using mechanical barriers to apply graded coatings to glass sheets.
U.S. Pat. No. 3,305,336 to Browne et al. discloses a spray gun system used in conventional spray techniques as opposed to electrostatic spray techniques, for applying a film on a glass surface. The film is formed as a band having a major area of maximum intensity bordered by a fade-out line that defines a fade-out area in which the transmittance of the film gradually and progressively increases until its value reaches the clarity of the glass substrate.
U.S. Pat. No. 4,138,284 to Postupack and U.S. Pat. No. 4,208,446 to Postupack et al., disclose a method of forming a graded shade band on a substrate by electrostatically spraying a dye composition past a grounded electroconductive shield or multiple grounded shield system toward a substrate to control the location of the cut-off line between the coated and uncoated regions of the substrate and to limit the amount of dye deposited in the vicinity of the cut-off line to form a graded coating.
Forming coatings, particularly metal oxide coatings, by spray pyrolysis is also known. For example, U.S. Pat. Nos. 3,660,061; 4,719,126 and 4,719,127, each of which are hereby incorporated herein by reference, describe the pyrolytic deposition of metal oxide films onto glass surfaces.
A relatively complex apparatus for forming coatings by spray pyrolysis is described in U.S. Pat. No. 4,111,150, which is hereby incorporated herein by reference. The apparatus is described as being able to obtain special effects in coatings, such as graded or varied thickness films by arranging sets of coating composition dispensers which are moved by a continuous traveling chain over a conveyor to coat glass traveling on the conveyor.
It would be advantageous to provide methods of and apparatus for forming pyrolytically deposited films or coatings having a fade zone, which methods and apparatus are in addition to those that are presently available and, more particularly, which do not require complex apparatus to obtain such a coating.
The present invention is directed to a method of forming a coating having at least one fade zone over a surface of a substrate. The present invention is also directed to an article which includes a substrate having a coating formed thereon, which coating includes at least one fade zone. Still further, the present invention is also directed to a novel apparatus for forming a coating having at least one fade zone over a surface of an article. In a preferred embodiment of the present invention, the coating is formed by the spray pyrolysis process.
The method for forming a coating having at least one fade zone over a surface of a substrate includes the steps of simultaneously directing a spray of a coating composition and a stream of a gas toward a surface of a substrate. The spray of coating composition and the stream of gas are maintained in spaced relation to one another such that an interference effect adjacent the surface of the substrate is produced between the spray of coating composition and the gas stream wherein the interference effect directs the coating composition to be deposited on the surface of the substrate as a coating having a fade zone. The method includes the step of depositing the coating composition over the surface of the substrate to form a coating having a fade zone over at least a portion of the surface of the substrate.
More particularly, the present invention includes a method for forming a coating having at least one fade zone over a surface of a substrate which method includes the steps of providing at least one coating composition dispenser above a surface of a substrate, wherein the coating composition dispenser is oriented to direct a spray of a coating composition toward the surface of the substrate, providing at least one gas dispenser above the surface of the substrate, wherein the gas dispenser is oriented to direct a stream of a gas toward the surface of the substrate. The method includes the steps of activating the coating composition dispenser to dispense a spray of coating composition and simultaneously activating the gas dispenser to dispense a stream of a gas. The spray of coating composition and the gas stream are maintained in spaced relation to one another such that an interference effect adjacent the surface of the substrate is produced between the spray of coating composition and the gas stream wherein the interference effect directs the coating composition to be deposited on the surface of the substrate as a coating having a fade zone. The method includes the step of depositing the coating composition over the surface of the substrate to form a coating having a fade zone over at least a portion of the surface of the substrate.
In an alternative embodiment of the present invention, the coating composition dispenser may be interposed between a pair of gas dispensers, all of the dispensers being positioned above a surface of a substrate wherein the spray of coating composition and the gas streams are maintained in spaced relation to one another such that an interference effect is produced adjacent the substrate surface between the spray of coating composition and the gas streams, wherein the coating composition is deposited over a surface of the substrate as a coating having a pair of opposed fade zones.
In yet another embodiment of the present invention a plurality of coating composition dispensers and gas dispensers may be provided above the surface of the substrate to provide a plurality of coatings on the surface of the substrate, at least a portion of the coatings including at least one fade zone. The present invention is also directed to a method for providing a coating having at least one fade zone on one or more discrete portions of a substrate surface.
The present invention is also directed to an article of manufacture which includes a substrate having at least one coating formed over a surface of the substrate, which coating includes at least one fade zone. In a preferred embodiment the substrate is glass, e.g. a glass float ribbon or an individual glass sheet, and the coating includes one or more metal oxide coatings, at least one or which includes a fade zone.
The present invention is also directed to an apparatus for depositing a coating having at least one fade zone on the surface of an article, which apparatus includes a device for moving an article in a downstream direction along an article movement path lying in a generally horizontal plane, a coating composition dispenser positioned in spaced relation above the article movement path wherein the coating composition dispenser directs a spray of coating composition downward toward the article movement path, and a gas dispenser positioned in spaced relation above the article movement path and spaced from the coating composition dispenser along a line generally perpendicular to the longitudinal axis of the article movement path wherein the gas dispenser directs a gas stream downward toward the article movement path. The coating composition dispenser and the gas dispenser are positioned relative to one another so as to produce an interference effect between the spray of coating composition and the gas stream which interference effect directs the coating composition to be deposited as a coating having at least one fade zone when directed toward the surface of an article conveyed along the article movement path.